I agree a bus conversion forum would probably be a better source for that info, though I think it's going to be difficult to find, electric fans aren't common conversions.
An alternative if you still have the original fan, shrouding and drive. With measurements from the fan, the number of blades, drive and driven pulley diameters to determine the fan operating RPM range old engineering manuals or a good manufacturers website might be able to give you a rough idea of CFM produced.
One other consideration, the fans move an incredible amount of air, which takes a lot of power. You're probably going to have to add an alternator to the engine dedicated to powering the fans.
Just my nickel if you're looking at an empty shell. You've got a couple of thousand hours of work ahead of you. GM and MCI spent thousands of hours designing a chassis and drive train that is dependable and works. Don't redesign it, go through it, look at every wear part and parts that don't normally wear. I'm guessing it has half a million miles if not more and there's a lot that could use attention. Make that reliable, there's not much worse than breaking down 1500 miles from home during a trip you've planned for months. Spend your engineering time, effort, and money on a killer interior. With the electronics today there are some amazing things you can do.